1) Ages of A + B + C end in the same digit as A + B, so C ends in a zero.

2) Ages of A + B start with same digit as A, so B is necessarily 0 through 9.

3) If an Age of 0 is allowed, then B and C could be newborn twins, and A is the odd man out.

4) If an Age of 0 is not allowed, but ages starting with zero are allowed, then C could be odd man out. For instance, Ambrose = Brandon = 4, and C is 90.

5) So I guess that we are supposed to assume that ages cannot be 0 and cannot start with a zero. In that case, B is 1 through 9 and cannot be the same as C (which ends in 0). And B cannot be the same as A, because A is more than 9. So B is the odd man out. Possible example: A = 10, C = 10, B = 5.